Methods of preparing casting moulds



J 1 L. PERAS 3,136,011

METHODS OF PREPARING CASTING MOULDS Filed Feb. 10, 1961 v Q F\NELY DWIDED ABRASWE m .,c' SUSPENSION m UQLHD I I PATTERN PLATE v CQSTING- \NLET I TO MOLD CRUST APTiR EEMOUAL FIG-.4-

$UPPORT T L r16 5 BACK up MATEQLAL- L causT' METAL LAYER CRUST J OUTER LAYER 0? Cu or AL (OPTIONAL) LAYER O CERMET LLAYEEEEPRACTOEY INVENTOR OXHDE 'LUCIEN Pizzas ATTORNEYS United States Patent Oifice Y 3,136,011 Patented June 9, 1964 3,136,011 METHODS OF PREPARING CASTING MOULDS Lucien Peras, Billancourt, Seine, France, assignor to Regie Nationale des Usines Renault, Billancourt, France Filed Feb. 10, 1961, Ser. No. 88,263

.Claims priority, application France Feb. 13, 1960 I 5 Claims. '(Cl. 2-2-113) This invention relates to methods of preparing casting moulds.

It is known that the casting of ferrous alloys, steel or cast-iron in metal or chill or die-casting moulds, or permanent metallic moulds, is attended by considerable ditficulties, whether the casting is effected by gravity, centrifugation or pressure injection. These difliculties lie more particularly in the risk of adherence or welding of the cast alloy to the metal of the mould walls, notably in the zones undergoing the maximum heating,

- that is where the mould is attacked by the jet of molten metal, and in the inner portions of the mould which project in the molten metal. Another difliculty arises from the strong thermal shock to which the mould is subjected as a consequence of the sudden contact with the molten metal heated. to a relatively high temperature, as this shock constitutes a sourceof incipient cracks, fissures, etc.

From the foregoing it appears that, to be satisfactory, a metal mould should have a number of technologically contradictory properties, such as a high degree of fireresistance or refractoriness, a high toughness in the hot state, and a good resistance to thermal shocks.

Now these exceptional properties are diificult to assemble in a single cast alloy.

It is the object of the present invention to provide a method of preparing permanent moulds in which all the inconveniences set forth hereinabove are definitely avoided. With the, moulds prepared according to the method of this invention it is possible to make a great number of accurate castings successively without deteriorating the moulds, so that a long useful life is obtained. It is an essential feature of this method to permit the preparation of moulds or mould elements of which the material consists either ofv a single layer or of successive layers closely adhering to one another, these layers consisting for example in succession of an oxide, a cermet (that is, a ceramic combined with a metal or alloy), a metal or an alloy. These different layers may be placed in the desired order, for example: an oxide in contact with the liquid bath of molten metal, then a cermet, and finally an alloy. The mould mateterial may also consist of a composition that cannot be cast, such as a cermet, but in all cases the mould is formed by spraying the material onto a pattern-forming plate by means of a commercial metallizing spraygun. The term pattern plate designates the replica of the mould or mould portion which it is desired to obtain; as a matter of fact, it may consist of a plate with bosses or bodies of revolution projecting thereon. The material sprayed onto the plate should form a layer of a thickness sufiicient to constitute a crust detachable from the pattern plate without breaking. This minimum thickness depends on the shape of the pattern plate but cannot be thinner than about .04". The spray guns suitable for carrying out this invention may be of the two conventional and known types, that is, with wire feed or powder feed. In the wire-feed gun the metal to be sprayed is fed to the spray nozzle in the form of a wire, in the case of ductile metals, and in the sintered state in the case of ceramic or cermet spraying. With the powder-feed spray-gun the materials to be sprayed are introduced in powder form into the spray-gun reservoir and fed therefrom by gravity-possibly with the assistance of vibration-to the spray nozzle. If desired, powders simply mixed together or powders from crushed alloys may be used indifferently.

The surface condition: of the pattern plate-which may consist of mild steel, for example, is extremely important; it should be neither too smooth nor too rough. On a polished pattern plate the particles sprayed by the gun will rebound without adhering; if the pattern plate'is sand blasted, the adherence is too high and it is not possible subsequently to remove the crust. A good surface condition is obtained by the so-called satinizing process which consists in applying to a metal part a jet of fine abrasive particles in suspension in Water (vapor blast). Of course, these pattern plates can be used for preparing a large number of crusts.

The invention will be further understood from the present description and from the drawings in which FIGURE 1 is a schematic view showing the condi tioning of a pattern plate;

FIGURE 2 is a view, partly in section, showing the formation of a crust by spraying;

FIGURE 3 is asimilar view showing the crust of FIG- URE 2 after it has been removed from the pattern plate;

FIGURE 4 is a view in section showing a casting mold formed by bringing two crusts into association; and

FIGURES 5 and 6 are views similar to FIGURE 2 showing a crust formed in more than one layer.

The preparation of mould crusts is effected as follows in practice: l

l) The pattern plate is prepared in the desired shape and made of steel, cast-iron or any other metal, by satinizing the surface with a fine abrasive substance preferably in suspension in water as shown in FIGURE 1.

(2) A metal oxide or cermet in a quantity suflicient to form a detachable crust is sprayed by using a spraygun onto this plate as shown in FIGURE 2. If desired, one or more layers of adequate composition may be sprayed e.g. as shown in FIGURES 4 and 6. It is not necessary to dress or otherwise prepare the surface prior to' spraying a layer of different composition onto a preceding layer. It may be advantageous, notably when the pattern plate comprises a surface of revolution, to impart a movement of rotation thereto, for example on a. lathe or the like, for building up the crust thereon by spraying. r

(3) The crusts are subsequently fitted and assembled in a mould as shown in FIGURE 4. The crusts are held in position either by tightly packing metal or refractory grains in a frame, or by using a preferably aluminous and porous cement, or by mechanical fastening in a metal mounting.

A mould may be constructed according to the method of this invention by using a crust consisting of a single layer of cermet, e.g. as depicted in FIGURE 2. The chromium composition with 40% (expressed in volume of compact material) of alumina or high-alumina bauxite is particularly adequate. In this case, in fact, the molten metal will contact mould walls having a high oxide content resulting from the high alumina content and the chromium oxide film which in all cases will be formed on the surface.

The metal portion of the mould is protected against the attack of the molten metal by the chromium and alumina oxides; these oxides offer to the metal an unbroken film resulting from the syncrystallization of C and A1 0 Departures from the precise conditions set forth herein by way of example may be made provided that the following ranges are adhered to when carrying out the method of this invention: Cr=l0% to70% of Al O expressed in volume of compact material.

Another possible process of preparing crusts of the type set forth hereinabove, in accordance with the method of this invention. consists in successively spraying a plurality of different layers to form a single crust c.g. as shown in FIGURES 5 and 6.

A specific embodiment illustrated partially in FIGURE 5 and giving satisfactory results from the dual point of view of crust elaboration and crust operation in a mould was obtained by spraying a first layer consisting of 82% Fe, 18% Cr with 25% (expressed in volume of compact material) of alumina or bauxite. This first layer having a minimum thickness of ca. .02 is coated with another layer sprayed from an alloy consisting of 80% Cr and 20% M0, and finally with a third layer of chromiumcontaining ferritic steel, 82% Fe and 18% Cr. The second and third layers have a substantially similar thickness ranging approximately from .04" to .4". Before operating a mould comprising a crust of this character a selective oxidation of the chromium content is'efiected with a view to form on the first layer contacting the molten metal a film having a high chromium oxide content reacting partially with the alumina of the cermet already in position. This selective oxidation may be effected, for example, by heating the crust to 1,200" F. in a humid hydrogen atmosphere.

If desired, departures from the exact conditions set forth hereinabove may be made, provided that the following limits are adhered to when carrying out the method of this invention:

First layer of Fe-Cr alloy containing 5% to 30% by weight of chromium, with to 60% alumina or bauxite expressed in volume of compact material.

Second layer of molybdenum and chromium, with 50% to 90% by weight of chromium.

Third layer of Fe-Cr alloy containing 5% to 30% by weight of chromium.

Another typical embodiment also illustrated in FIG- URE 6 of a multiple-layer crust for moulds consists in spraying firstly onto the pattern plate a film of pure refractory oxide without metal. This layer adheres very satisfactorily to the next layer having a metal support. A solution cited hereafter by way of example and having given satisfactory results consists in spraying a first, thin layer of alumina of a thickness ranging from ca. .002" to .004", then spraying onto this layer a cermet containing 66% Cr, Mo, 14% Fe and, in addition, 20% of alumina expressed in volume of compact material. The third or external layer consists of 82% Fe and 18% Cr, or any other stainless ferrous alloy. The second layer and third layer have together a thickness ranging from .08" to If desired, departures from the exact figures given hereinabove by way of example may be made, provided that the method is carried out within the following limits:

Second layer: 50% to 80% Cr; 10% to 45% Mo; 5% to Fe by weight, and 5% to A1 0 or bauxite, expressed in volume of compact material.

Third layer: Fe with 5% to 30% of Cr.

To take due account of the heat transfer phenomena of which the occurrence is well known in metal casting, the crusts of the difierent types set forth hereinabove, which are obtained according to the method of this invention, may be coated with a thick secondary sprayed layer of copper or aluminum e.g. as shown in FIGURE 6 with a view to promote a quick dissipation of the heat transferred from the molten metal through the primary layer or layers adapted to withstand the detrimental action of thermal shocks and the attacks from the molten metal. Conversely, a layer of alumina or magnesia may be introduced be tween, or applied externally of, the primary layers with a view to retard the dissipation of the heat delivered by the molten metal. This heat dissipation may be accelerated or retarded according to the type of metal cast in the mould, the mass of the final casting and also its shape. It is also possible, in a same mould, to have some portions where the heat dissipation is accelerated and other portions where the heat dissipation is retarded.

Alternately, in the three crust compositions described herein the side contacting the molten metal may be coated with a conventional protective film applied periodically either with a brush, or by spraying a cloud of dust, or with a blower, a smoky flame, many other conventional means. The coating may consist of alumina, silica, silico-aluminate, graphite, lamp black, acetylene black, etc.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. A crust suitable for use in moulds and mould parts for casting metals and alloys comprising a cermet formed by spraying a mixture of a metal and a ceramic oxide onto a metal pattern plate.

2. A crust according to claim 1 containing additional layers of metal and ceramic oxide sprayed thereon.

3. A crust according to claim 1 having an additional layer of copper or aluminum sprayed thereover to accelerate heat transfer therethrough.

4. A crust according to claim 1 wherein the metal is a ferritic iron and chromium alloy and the ceramic oxide is alumina.

5. A crust according to claim 1 formed by successively spraying a first layer consisting of alumina and having a thickness of circa 0.002 to 0.04"; a second layer consisting of a cermet comprising a metal component containing by weight 50 to chromium, 10 to 45% molybdenum, 5 to 25% iron and an alumina ceramic component in the proportion of 5 to 40% expressed in volume of compact material; and a third and external layer consisting of a ferritie chromium alloy containing from 5 to 30% by weight of chromium References Cited in the file of this patent UNITED STATES PATENTS 1,912,889 Couse June 6, 1933 1,935,916 Ragsdale Nov. 21, 1933 2,171,599 Reid Sept. 5, 1939 2,303,092 Raphael Nov. 24, 1942 2,479,598 Barber et al Aug. 23, 1949 2,609,576 Roush et al Sept. 9, 1952 2,734,243 Lips et al Feb. 14, 1956 2,806,271 Operhall Sept. 17, 1957 2,880,486 Wallace Apr. 7, 1959 

1. A CRUST SUITABLE FOR USE IN MOULDS AND MOULD PARTS FOR CASTING METALS AND ALLOYS COMPRISING A CERMET FORMED BY SPRAYING A MIXTURE OF A METAL AND A CERAMIC OXIDE INTO A METAL PATTERN PLATE. 